Peptide injections into the amygdala of conscious rats: effects on blood pressure, heart rate and plasma catecholamines

Neuropeptide changes following excitotoxic lesion of the insular cortex in rats

Following middle cerebral artery occlusion in Wistar rats, the immunoreactivity of neuropeptide Y increased ipsilaterally in the insular cortex and basolateral nucleus of the amygdala. In addition, the immunoreactivity of leucine-enkephalin, dynorphin, and neurotensin increased in the ipsilateral central nucleus of the amygdala. The amygdalar neurochemical changes are likely the result of damage to the insular cortex, although other cortical areas were also affected by the ischemia. To investigate whether damage to the insular cortex is essential in eliciting these changes, a localized lesion of the right or left insular cortex was produced by microinjection of D,L-homocysteic acid. Control animals received injections of vehicle into the right or left insular cortex or D,L-homocysteic acid into the right primary somatosensory cortex. Neurochemical changes were examined immunohistochemically with the peroxidase-antiperoxidase reaction 5 days after the injection. The immunoreactivity of neuropeptide Y increased locally after excitotoxic damage to the insular cortex or primary somatosensory cortex. The amygdalar neurochemical changes, including neuropeptide Y increase in the basolateral nucleus and leucine-enkephalin, dynorphin, and neurotensin increase in the central nucleus, were seen only when the ipsilateral insular cortex was lesioned. These neurochemical changes were similar to those seen 5 days after middle cerebral artery occlusion. Our findings indicate that damage to the insular cortex is essential in eliciting the neurochemical changes in the ipsilateral amygdala. In addition, the change in neuropeptide Y in the cortex appears to be a local reaction occurring irrespective of location of the lesion and glutamate receptor activation may be involved.

Neurochemical changes following occlusion of the middle cerebral artery in rats

We have developed a stroke model involving middle cerebral artery occlusion in the rat which elicits changes in cardiac and autonomic variables that are similar to those observed clinically. It is likely that these neurogenic autonomic responses are mediated by changes in neurotransmitter systems subsequent to the stroke. This possibility was investigated by examining changes in immunohistochemical staining for tyrosine hydroxylase, neuropeptide Y, leu-enkephalin, neurotoxins and dynorphin following middle cerebral artery occlusion in the rat. Computerized image analysis was used to provide semi-quantitative measurements of the changes. The ischemic region was centered primarily in the insular cortex. The results indicate that there are significant increases in immunostaining for tyrosine hydroxylase and neuropeptide Y in the insular cortex within the peri-infarct region. Neuropeptide Y staining was also significantly increased in the basolateral nucleus of the amygdala, ipsilateral to the middle cerebral artery occlusion, which did not appear to be included in the infarct. Leu-enkephalin, neurotensin and dynorphin staining was significantly elevated in the central nucleus of the amygdala ipsilateral to the occlusion of the middle cerebral artery. These neurochemical changes are discussed as possible mechanisms mediating the cardiac and autonomic consequences of stroke or as part of a process to provide neuro-protection following focal cerebral ischemia.

Time-course of neuropeptide changes in peri-ischemic zone and amygdala following focal ischemia in rats

Previously, using a middle cerebral artery occlusion model in Wistar rat, we showed autonomic disturbances similar to those seen clinically and observed striking neurochemical changes in cortical and subcortical sites at 5 days following stroke. The neurochemical changes may account for functional recovery and/or autonomic disturbances after focal ischemia. To understand the possible mechanisms and to facilitate future studies, it is necessary to define the time-courses of these changes. Using immunohistochemical staining with the peroxidase-antiperoxidase reaction, the changes in several neuropeptides over the peri-ischemic region and the ipsilateral central and basolateral nucleus of the amygdala were investigated at different times after middle cerebral artery occlusion. In the experimental group, neuropeptide Y immunoreactivity appeared to increase by 6 hours in the peri-ischemic region. Using image analysis to quantify the staining intensity, the change became statistically significant at 1 day, peaked around 3 days, and subsided at 10 days. There was a delayed increase in neuropeptide Y in the ipsilateral basolateral nucleus of the amygdala with a peak around 3 days. Immunoreactive staining for leucine-enkephalin, dynorphin, and neurotensin demonstrated an increase that was localized to the ipsilateral central nucleus of the amygdala with a peak around 3 days and a return to baseline levels by 10 days. The results support a specific time-course for each of the neuropeptides studied and indicate that a survival time of 3 days after focal ischemia is the critical period for examining the relationship between neuropeptide responses and neuronal or functional recovery.

Restraint stress increases corticotropin-releasing hormone mRNA content in the amygdala and paraventricular nucleus

Corticotropin-releasing hormone (CRH) neurons located in the paraventricular nucleus (PVN) of the hypothalamus are implicated in regulating the endocrine response to stress. The amygdala is an established component of the neural circuitry mediating the stress response. To obtain information concerning the effects of stress on amygdala CRH neurons, a time-course study was conducted to examine, in rats, whether a 1-h restraint period increases CRH mRNA levels. The effects of restraint were also measured in the PVN. Using a sensitive RNase protection assay, we found that CRH mRNA levels in both the amygdala and paraventricular nucleus were significantly elevated 1 h after cessation of restraint. CRH mRNA levels in the paraventricular nucleus, but not the amygdala, remained elevated at the 3-h post-stress interval. 48 h after the termination of restraint, CRH mRNA levels in both brain structures returned to control levels. These data provide the first direct evidence that stress activates amygdala CRH neurons.

Dietary calcium and blood pressure in experimental models of hypertension. A review

More than 80 studies have reported lowered blood pressure after dietary calcium enrichment in experimental models of hypertension. The evidence presented here suggests that dietary calcium may act concurrently through a number of physiological mechanisms to influence blood pressure. The importance of any given mechanism may vary depending on the experimental model under consideration. Supplemental dietary calcium is associated with reduced membrane permeability, increased Ca(2+)-ATPase and Na,K-ATPase, and reduced intracellular calcium. These results suggest that supplemental calcium may limit calcium influx into the cell and improve the ability of the VSMC to extrude calcium. This could be a direct effect of calcium on the VSMC or an indirect effect mediated hormonally. The calcium-regulating hormones have all been found to have vasoactive properties and therefore may influence blood pressure. Furthermore, CGRP and the proposed parathyroid hypertensive factor are both vasoactive substances that are responsive to dietary calcium. Therefore, diet-induced variations in calcium-regulating hormones may influence blood pressure. Modulation of the sympathetic nervous system is another important way that dietary calcium can influence blood pressure. There is evidence of altered norepinephrine levels in the hypothalamus as a consequence of manipulations of dietary calcium as well as changes in central sympathetic nervous system outflow. Dietary calcium has also been shown to specifically modify alpha 1-adrenergic receptor activity in the periphery. In some experimental models of hypertension, dietary calcium may alter blood pressure by changing the metabolism of other electrolytes. For example, the ability of calcium to prevent sodium chloride-induced elevations in blood pressure may be attributed to natriuresis. However, natriuresis does not account for all of the interactive effects of calcium and sodium chloride on blood pressure. Sodium chloride-induced hypertension may be due in part to calcium wasting and subsequent elevation of calcium-regulating hormones. Chloride is an important mediator of this effect because it appears that sodium does not cause calcium wasting when it is not combined with chloride. More attention to the central nervous system effects of dietary calcium is needed. Not only can calcium itself influence neural function, but many of the calcium-regulating hormones appear to affect the central nervous system. The influence of calcium and calcium-regulating hormones on central nervous system activity may have important implications for blood pressure regulation and also may extend to other aspects of physiology and behavior.

Corticotropin releasing factor neurons are innervated by calcitonin gene-related peptide terminals in the rat central amygdaloid nucleus

The central nucleus of the rat amygdala (CeA) contains many corticotropin releasing factor (CRF) immunoreactive neurons. Previous studies have demonstrated that these CRF neurons project to brain stem regions responsible for modulation of autonomic outflow. Calcitonin gene-related peptide (CGRP) terminals overlap the distribution of CRF cell bodies in the CeA. These CGRP terminals mainly originate from cell bodies that are located in the pontine parabrachial nucleus. The present study examined the possibility that CRF cell bodies are innervated by CGRP terminals. The results suggest that over 35% of the CRF neurons in the CeA are contacted by CGRP terminals as judged by the indiscernible distances between the terminals and cell bodies and or dendrites. In addition, a dual-labeled electron microscopic technique demonstrates that CGRP terminals form synaptic contacts with CRF cell bodies and dendrites. This suggests that CGRP neurons in the parabrachial nucleus can modulate the activity of CRF amygdaloid brain stem efferents. Previous studies have shown that CRF, when administered into the central nervous system, produces increases in heart rate, blood pressure, and plasma catecholamines. CGRP administration into the amygdala has been shown to have a similar effect on the autonomic nervous system. It is, therefore, possible that CGRP could exert these effects via an amygdaloid CRF pathway.

Short-term effects of somatostatin analogue (SMS 201-995) on left ventricular function in healthy persons: a scintigraphic study

Since somatostatin has been reported to have a negative inotropic and chronotropic effect on atria and positive inotropic effect on ventricle, present study was designed to investigate the acute effects of somatostatin analogue SMS 201-995 infusion on the left ventricular function in healthy volunteers. After labeling the autologous red blood cells with 750-1000 MBq 99mTc-pertechnetate, ECG-gated radionuclide ventriculography was performed. Using Fourier analysis of the left ventricular time-activity curve, ejection fraction (EF), peak ejection rate (PER), peak filling rate (PFR), time to end-systole (TES) and normalized TES/T values were calculated. Study group consisted of 12 healthy volunteers. Somatostatin analogue SMS 201-995 infusion was given at a rate of 100 micrograms/h during 2h. Baseline, 1st, 2nd h and 4th h imagings were done using the same protocol. Simultaneously heart rate and blood pressure were recorded. The difference between parameters was tested using Kruskall-Wallis test. The mean heart rate, systolic and diastolic blood pressures and did not show any statistically significant change during the somatostatin analogue infusion and 2h later in comparison to baseline values. The mean PER and PFR had a slight decrease at the first hour of infusion, but the change was not significant. However, the significant correlation of PER values with heart rate, EF and TES observed at baseline study were disappeared during the infusion. These results indicate that somatostatin analogue infusion does not appear to change the left ventricular systolic and diastolic function in healthy persons significantly.

Amygdaloid CRF pathways. Role in autonomic, neuroendocrine, and behavioral responses to stress

The results of numerous studies have provided compelling evidence that CRF plays an important function in the amygdala. Stimulation of the amygdala produces physiological changes similar those observed after central injections of CRF. Central injections of CRF activate neurons in the amygdala as measured by increases in c-fos protein expression. Destruction of cells or injections of CRF antagonist in the amygdala can attenuate some of the central effects of CRF. The amygdala is the origin of major CRF-containing pathways in the brain. Amygdaloid CRF neurons project to widespread regions of the basal forebrain and brain stem. These amygdaloid pathways mainly arise from the central amygdaloid nucleus where there are a large number of CRF immunoreactive neuronal perikarya. Glucocorticoid and CRF-binding protein are located in cells of the central amygdaloid nucleus. CRF neurons in the central nucleus send their axons to the bed nucleus of the stria terminalis, lateral hypothalamus, midbrain central gray, raphe nuclei, parabrachial region, and the nucleus of the solitary tract. Tract tracing studies have suggested that amygdaloid CRF neurons also innervate CRF neurons in some of these regions and, furthermore, that CRF neurons in some of these areas project back to the CRF neurons in the amygdala. Thus, the amygdala is part of a network of brain nuclei interconnected by CRF pathways. In addition, amygdaloid CRF neurons may project directly to dopaminergic, noradrenergic, and serotonergic neurons, which have widespread projections throughout the neuroaxis.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing hormone microinfusion in the central amygdala diminishes a cardiac parasympathetic outflow under stress-free conditions

The central nucleus of the amygdala (CeA) is known to be involved in the regulation of autonomic, neuroendocrine and behavioural responses in stress situations. The CeA contains large numbers of corticotropin-releasing hormone (CRH) cell bodies. Neuroanatomical studies revealed that the majority of the CRH fibres from the CeA have direct connections with autonomic regulatory nuclei in the brainstem. In the present study, the effects of locally infused CRH (30 ng) into the CeA, in freely moving male Wistar rats under stress-free conditions, were examined. Heart rate, endocrine parameters and behavioural activity were repeatedly measured before, during and after local administration of CRH, pretreated with either artificial CSF or the CRH-receptor antagonist, alpha-helical CRH (alpha-hCRH). CRH infusion alone caused a long-lasting increase in heart rate without affecting plasma adrenaline and noradrenaline as indicators of sympathetic activity. This CRH-induced tachycardia was effectively blocked by pretreatment with a high dose (1 microgram) alpha-hCRH locally into the CeA, while the pretreatment with low dose (0.1 microgram) of the alpha-hCRH caused a minor blockade of the CRH-induced tachycardia. The results suggest that CRH mechanisms in the CeA regulate the autonomic changes probably only by affecting parasympathetic but not sympathetic output systems. Because CRH is given at the level of the cell body of the CRH neurons in the CeA, we suggest that the reduction of the parasympathetic output may be explained as an autoreceptor-mediated inhibition of CRH neurons from the CeA with parasympathetic-regulating brainstem nuclei.

Autonomic areas of rat brain exhibit increased Fos-like immunoreactivity during opiate withdrawal in rats

We sought to identify the brain areas that might contribute to the increased autonomic activity seen during morphine withdrawal by mapping neuronal expression of c-fos protein (Fos) and Fos-related antigens. Rats were implanted with morphine pellets or placebo pellets over a 5 day regimen and injected on day 6 with either saline or naltrexone (100 mg/kg). After a standard PAP immunocytochemical protocol, Fos-like immunoreactivity (Fos-LIR) was observed in medullary nuclei including the NTS (nucleus of the solitary tract), caudal (CVL) and rostral ventrolateral medulla (RVL). Although some Fos-LIR was seen in these areas in control rats (either morphine-implanted, saline injected, or placebo-implanted, saline or naltrexone injected), a significantly higher number of Fos-LIR-positive cells in NTS, CVL and RVL were seen after morphine withdrawal. Large numbers of Fos-like immunoreactive cells were also seen in the A5 area, the parabrachial nuclei of the pons and the locus coeruleus. Increased Fos-LIR was also detected in the paraventricular nucleus of the hypothalamus and the amygdala of morphine withdrawn rats. The Fos-LIR was co-localized with tyrosine hydroxylase immunoreactivity in many of the cells in caudal and rostral ventrolateral medulla, A5 and locus coeruleus. These data support the conclusion that autonomic areas in brain and noradrenergic/adrenergic cells in these areas are activated during morphine withdrawal and may contribute to the autonomic symptoms of opiate withdrawal.

Attenuation of stress-induced behavior by antagonism of corticotropin-releasing factor receptors in the central amygdala in the rat

Research suggests that endogenous corticotropin-releasing factor (CRF) in the amygdala plays a role in the expression of stress-induced behavior. This study examined in rats whether antagonism of CRF receptors in the central amygdala (CA) region using alpha-helical CRF9-41, a CRF antagonist, was effective in attenuating the occurrence of stress-induced freezing. Bilateral infusions of 50, 100, or 200 ng of the CRF antagonist were made in the CA region using 33-gauge cannula immediately prior to testing. Freezing was measured in two test conditions. In one condition, the effects of the CRF antagonist on freezing was assessed immediately after exposure to electric foot shock. In the other condition, freezing was examined in shock-experienced rats that were re-exposed to the shock environment. Results suggested that 50 and 100 ng of the CRF antagonist were effective in reducing the duration of freezing in the immediate post-shock period. In addition, the 100 ng dose produced a significant reduction in freezing duration after rats were re-exposed to the shock environment. Collectively, data suggest that antagonizing the action of endogenous CRF in the CA region contributes to a general alleviation of stress-induced freezing.

Intracerebroventricular administration of corticotropin-releasing factor induces c-fos mRNA expression in brain regions related to stress responses: comparison with pattern of c-fos mRNA induction after stress

Centrally administered corticotropin-releasing factor (CRF) produces a number of physiological and behavioral changes akin to those elicited by exposure to acute stress. However, the specific brain site of action responsible for the centrally activating property of CRF has not been precisely determined. In this study, we used in situ hybridization histochemistry for c-fos mRNA to map potential neuronal structures activated after intracerebroventricular (i.c.v.) injection of CRF and compared the distribution of c-fos mRNA with that after stress. Wistar male rats were sacrificed 30, 60, 120 and 180 min after the i.c.v. injection of 1 microgram ovine CRF or vehicle alone. Another group of rats was exposed to immobilization stress for 60 min or electrical foot-shock stress (1.5 mA, 1-s duration, 30 x) for 15 min and sacrificed before and 30, 60, 120 and 180 min after the beginning of stress. Centrally administered CRF rapidly (30-60 min) induced c-fos mRNA expression in most of the areas that showed hybridization signals for c-fos after stress: the limbic structures, including the piriform cortex, cingulate cortex, the lateral septal nucleus, the hippocampus, the anterior corticomedial and the medial amygdaloid nuclei, the hypothalamic nuclei, such as the paraventricular nucleus, the supraoptic nucleus (SO) and the dorsomedial nucleus (DMD), and some brainstem nuclei like the pontine nucleus, the locus ceruleus (LC) and Barrington's nucleus. The granular layer of the cerebellum, some thalamic nuclei and the habenula also showed hybridization signals after i.c.v. injection of CRF and stress. However, c-fos induction in the bed nucleus of the stria terminalis, the central nucleus of the amygdala (CeA) and the nucleus tractus solitarius (SOL) was seen only after i.c.v. administration of CRF; in the septo-hypothalamic nucleus and the superior olive, however, c-fos mRNA expression was observed only after stress. There were no differences in the pattern of c-fos mRNA expression between the two stress paradigms. In contrast, i.c.v. injection of saline-induced expression of c-fos mRNA in the piriform cortex, neocortex, cingulate cortex and the amygdala was much less than that seen after i.c.v.-administered CRF as evident in the intensity of the signals. These results suggest that CRF produces c-fos mRNA expression in the brain areas related to stress response, and that CRF may induce behavioral and neuroendocrine responses through activating these brain structures, such as the limbic system and the hypothalamic nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Co-localization of peptide-like immunoreactivities with glucocorticoid receptor- and Fos-like immunoreactivities in the rat parabrachial nucleus

The parabrachial nucleus (PB) is a brainstem nucleus, which mediates autonomic information from the viscera to various forebrain nuclei, e.g. to the central nucleus of the amygdala (ACe) and to the medial preoptic area (MPOA). The neurons of the PB contain several neuropeptides, of which calcitonin-gene related peptide-immunoreactive (CGRP-IR) and neurotensin (NT)-IR neurons provide input to the ACe, whereas corticotropin-releasing factor-IR (CRF) neurons project to the MPOA. The aim of the present paper was to study whether the neurons containing CGRP-, NT- and CRF-like immunoreactivities (LIs) in the PB also contain glucocorticoid receptor (GR)- and/or Fos-LIs after stress. No co-localization was observed with the GR-LI and peptide-LIs, suggesting that plasma glucocorticoids do not have direct effects on these neurons of the PB. After stress, the vast majority of the peptide-IR perikarya exhibited Fos-LI, suggesting that the peptidergic pathways from the PB to ACe and MPOA are activated in stress. The ACe and MPOA have been connected in various stress related responses, e.g. inhibiting the hypothalamo-pituitary-gonadal axis, raising the blood pressure and pulse, and increasing the secretion of glucocorticoids. Therefore, the activation of the peptidergic pathways between the PB and the ACe and MPOA suggests that some of these responses may be elicited by the peptidergic input from the PB. Furthermore, since Fos acts as a transcription factor, stress may affect the expression of the neuropeptides studied.

Marked species-difference in the vascular angiotensin II-forming pathways: humans versus rodents

Using isolated arteries, we demonstrated a marked difference in the angiotensin II-forming systems between human and rodent vessels. In human arteries, only 30-40% of the conversion of angiotensin I to angiotensin II depended on the angiotensin-converting enzyme (ACE), and the rest of the angiotensin II formation was ascribed to chymostatin-sensitive angiotensin II-generating enzyme (CAGE). On the contrary, angiotensin II formation in rodent arteries totally depended upon ACE, without any sign of CAGE involvement. Such a marked species-difference can be relevant to the reported difference between humans and rodents in the ACE inhibitor effects on the myointimal hyperplasia after intimal balloon injury.

The central nucleus of the rat amygdala: in vitro intracellular recordings

Membrane properties of neurons from the central nucleus of the rat amygdala (ACe) were analyzed using intracellular current-clamp recordings from in vitro coronal slices of adult rat amygdala. Two types of neurons were identified and classified according to their accommodation characteristics and the nature of their afterhyperpolarizations (AHP). Type A neurons represented 74% of the population and were identified by a lack of accommodation and a medium-AHP (m-AHP) in response to transient (100 ms) depolarizing current injection. The m-AHP was defined by a fast decay time constant with a mean tau AHP = 113.6 ms. In both Type A and Type B ACe cells the m-AHP can be reduced with cadmium and rubidium. Type B neurons represented 26% of the population and were identified by the presence of accommodation and a long duration slow-AHP (s-AHP) following the m-AHP. The s-AHP was defined by a slow decay time constant with a mean tau AHP = 1.7 s. The s-AHP was similar to the AHP mediated by IAHP, a long duration calcium-dependent, noradrenaline-sensitive current present in hippocampal neurons. In Type B cells, the s-AHP was reduced by cadmium and noradrenaline. There was no significant difference between Type A and B ACe neurons in passive electrical properties such as the membrane input resistance (RiA = 113 M omega, RiB = M omega), and the membrane time constant (tau A = 15 ms, tau B = 16 ms). However, there was a statistically significant difference in the resting membrane potentials of Type A and B ACe neurons (RMPA = -67 mV; RMPB = -63 mV). These data suggest that the characteristic active membrane properties displayed by Type A and Type B neurons will determine the ability of each type to integrate and encode neuronal information.

Cardiac, neuroendocrine, and behavioral effects of central amygdaloid vasopressinergic and oxytocinergic mechanisms under stress-free conditions in rats

The central nucleus of the amygdala (CEA) is considered to play a major role in the expression of behavioral, autonomic, and neuroendocrine components of the stress response. The present study was designed to examine possible modulating effects of the neuropeptides arginine-8-vasopressin (AVP) and oxytocin (OXT) on functioning of the CEA in male Wistar rats. Heart rate, neuroendocrine parameters, and behavioral activity were repeatedly measured before, during, and after local administration of several doses of AVP and OXT under stress-free resting conditions. In comparison with control artificial-CSF infusion, AVP infusion in the lowest dose (20 pg) caused in a part of the animals a long-lasting decrease in heart rate, i.e., bradycardia, without affecting behavioral activity. In contrast, local infusion with high doses of AVP and OXT (2 ng) induced a transient cardioacceleration concomitant with an increase in behavioral activity. Moreover, these latter effects of AVP could effectively be blocked by pretreatment with a selective OXT receptor antagonist. These findings suggest that higher doses of AVP are effective via agonistic action on OXT receptors in the CEA. A strong correlation existed between the magnitudes of the tachycardiac response and behavioral activation. Thus, heart rate increase by OXT receptor stimulation is possibly due to somatic-autonomic coupling rather than genuine autonomic activation. Additionally, plasma corticosterone, but not epinephrine and norepinephrine, concentrations were elevated in response to AVP and OXT infusions. In conclusion, these results suggest that vasopressinergic influences on CEA function involve two receptor mechanisms possibly related to differential output systems.

Colocalization of peptide- and tyrosine hydroxylase-like immunoreactivities with Fos-immunoreactive neurons in rat central amygdaloid nucleus after immobilization stress

The central amygdaloid nucleus (ACe) is part of the amygdaloid body, and it has been shown to participate in several stress related reactions. The ACe is densely innervated by tyrosine hydroxylase- (TH), corticotropin releasing factor- (CRF), calcitonin gene-related peptide- (CGRP), neurotensin- (NT), somatostatin- (SOM), enkephalin- (ENK), substance P- (SP), vasoactive intestinal polypeptide- (VIP) and cholecystokinin- (CCK) immunoreactive (IR) nerve terminals. In addition, the ACe contains numerous CRF-, NT-, SOM-, ENK- and SP-IR perikarya. In previous studies it has been shown that stress stimulates the expression of the immediate early gene c-fos in the ACe. The aim of this study was to demonstrate the colocalization of the Fos-IR neurons with the peptide- and TH-IR structures using an immunocytochemical double staining technique. In intact animals the ACe contained only a few Fos-IR neurons. After immobilization stress about 100 Fos-IR neurons were seen per section. They were mainly located in the area, which was enriched by peptide- and TH-IR nerve terminals. The close contacts observed between the Fos-IR neurons and the peptide- and TH-IR nerve endings suggest that the Fos-IR neurons were innervated by these nerve terminals. Furthermore, several NT-, ENK-, SOM- and CRF-IR neurons were observed and the vast majority of these cells exhibited Fos-like immunoreactivity. These results suggest that stress enhances the synaptic activity of the ACe, which stimulates the expression of c-fos. Subsequently, Fos may regulate the expression of the NT, ENK, SOM and CRF genes and thus affect the peptidergic efferents from the ACe.

Vasopressinergic modulation of stress responses in the central amygdala of the Roman high-avoidance and low-avoidance rat

The central nucleus of the amygdala (CEA) is selectively involved in the passive component of the behavioral (immobility) and the accompanying parasympathetic response during conditioned, stressful environmental challenges. Vasopressinergic mechanisms in the brain seem to play a role in these stress responses. The effects of the neuropeptides arginine-8-vasopressin (AVP) and oxytocin (OXT) on modulating CEA activity during conditioned stress of inescapable footshock were studied in male Roman high-avoidance (RHA/Verh) and low-avoidance (RLA/Verh) rats, psychogenetically selected on the basis of shuttle-box acquisition behavior. In RLA/Verh rats, the cardiac and behavioral responses to the conditioned emotional stressor were bradycardia and immobility, suggesting an important role for the CEA in these rats. The RHA/Verh rats, however, failed to show any change in heart rate or immobility in response to a conditioned stress situation. The low dose of AVP (20 pg) in the CEA of conscious RLA/Verh rats caused an enhancement of the stress-induced bradycardiac and immobility response. However, the high dose of AVP (2 ng) and OXT (200 pg) attenuated the bradycardiac and immobility responses in the RLA/Verh rats. Infusion of AVP and OXT in the RHA/Verh rats failed to induce any change in heart rate or immobility. Binding studies revealed that the AVP receptor selectively binds AVP with high affinity. In contrast, the OXT receptor recognizes both AVP and OXT with a similar (but lower) affinity. This suggests that the behavioral and autonomic responses of the high dose of AVP may be caused by OXT receptor stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptide immunoreactive neurons in the amygdala and the bed nucleus of the stria terminalis project to the midbrain central gray in the rat

The central nucleus of the amygdala, bed nucleus of the stria terminalis, and central gray are important components of the neural circuitry responsible for autonomic and behavioral responses to threatening or stressful stimuli. Neurons of the amygdala and bed nucleus of the stria terminalis that project to the midbrain central gray were tested for the presence of peptide immunoreactivity. To accomplish this aim, a combined immunohistochemical and retrograde tracing technique was used. Maximal retrograde labeling was observed in the amygdala and bed nucleus of the stria terminalis after injections of retrograde tracer into the caudal ventrolateral midbrain central gray. The majority of the retrogradely labeled neurons in the amygdala were located in the medial central nucleus, although many neurons were also observed in the lateral subdivision of the central nucleus. Most of the retrogradely labeled neurons in the BST were located in the ventral and posterior lateral subdivisions, although cells were also observed in most other subdivisions. Retrogradely labeled neurotensin, corticotropin releasing factor (CRF), and somatostatin neurons were mainly observed in the lateral central nucleus and the dorsal lateral BST. Retrogradely labeled substance P-immunoreactive cells were found in the medial central nucleus and the posterior and ventral lateral BST. Enkephalin-immunoreactive retrogradely labeled cells were not observed in the amygdala or bed nucleus of the stria terminalis. A few cells in the hypothalamus (paraventricular and lateral hypothalamic nuclei) that project to the central gray also contained CRF and neurotensin immunoreactivity. The results suggest the amygdala and the bed nucleus of the stria terminalis are a major forebrain source of CRF, neurotensin, somatostatin, and substance P terminals in the midbrain central gray.

Organization of amygdaloid projections to brainstem dopaminergic, noradrenergic, and adrenergic cell groups in the rat

The distribution of amygdaloid axons in the various brainstem dopaminergic, noradrenergic, and adrenergic cell groups was examined. This was accomplished by means of the Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing technique combined with glucose-oxidase immunocytochemistry to catecholamine markers (i.e., tyrosine hydroxylase, dopamine beta hydroxylase, and phenylethanolamine N-methyltransferase). Injections of PHA-L in the medial part of the central amygdaloid nucleus resulted in axonal and terminal labeling in most catecholamine cell groups in the brainstem. Amygdaloid terminals appeared to contract catecholaminergic cells in several brainstem regions. The most heavily innervated catecholaminergic cells were the A9 (lateral) and A8 dopaminergic cell groups and the C2/A2 adrenergic/noradrenergic cell groups in the nucleus of the solitary tract. The medial part of the A9 and adjacent A10 dopaminergic cell groups was moderately innervated. A moderate innervation by amygdaloid terminals was observed on rostral locus coeruleus noradrenergic cells (A6 rostral) and adrenergic cells of the rostral ventrolateral medulla (C1). Noradrenergic cells of the A5, main body of the locus coeruleus (A6), A7, and subcoeruleus were sparsely innervated. Amygdaloid axons were not observed on noradrenergic neurons of the A4 cell group, area postrema, and A1 cells of the ventrolateral medulla. The results demonstrate that the amygdala primarily innervates the dopaminergic cells of midbrain (i.e., A8 and lateral A9 cells) and the adrenergic cells (C2) and noradrenergic (A2) cells in the nucleus of the solitary tract. The possible functional significance of amygdaloid innervation of catecholaminergic cells is discussed.

Glutamate-immunoreactive neurons of the central amygdaloid nucleus projecting to the subretrofacial nucleus of SHR and WKY rats: a double-labeling study

Glutamate immunoreactivity was found in 9%, in the case of Wistar Kyoto rats (WKY), and 14%, in the case of spontaneously hypertensive rats (SHR), of neurons located in the medial division of the central amygdaloid nucleus (CeM) projecting ipsilaterally to the subretrofacial nucleus (SRF) in the rostral ventrolateral medulla using a double-labeling technique in combination with glutamate immunocytochemistry. The results indicate that possibly-glutamatergic neurons located in the CeM project to the SRF, in which vasomotor neurons are present, suggesting involvement of the CeM in blood pressure regulation. No significant difference was found between the distribution of labeled CeM neurons in SHR and WKY rats.

Rat central amygdaloid nucleus projections to the bed nucleus of the stria terminalis

The projections from the central amygdaloid nucleus (Ce) to different subdivisions of the bed nucleus of the stria terminalis (BNST) were investigated using retrograde transport of fluorescent dyes. Iontophoretic injections of either Fast Blue (FB) or bisbenzimide (BB) were applied to the anterior medial, posterior medial, anterior lateral and posterior lateral parts of the bed nucleus of the stria terminalis. The anterior medial BNST receives projections from caudal part of medial Ce (CeM). The posterior medial BNST receives projections specifically from the intermediate subdivision of Ce, though in some cases projections from the ventral subdivision (CeV) of Ce were seen. The anterior lateral BNST receives projections primarily from the caudal lateral Ce (CeL) as well as middle and caudal part of CeM. The posterior lateral BNST receives projection from rostral CeL as well as the CeV and lateral capsular Ce. In general, the results indicate that the major subdivisions of the BNST receive projections from Ce subdivisions having similar connections with diencephalic or brainstem cell groups. Additional evidence is presented suggesting that Ce-BNST projections are part of an extensive system of intrinsic connections linking similar groups of neurons in both the Ce and BNST as well as within Ce.

Central amygdala lesions affect behavioral and autonomic balance during stress in rats

The effects of a bilateral electrolytical lesion of the CEA on the behavioral and sympathetically induced cardiac response in the shock-probe/defensive-burying test have been analyzed in male Wistar rats. Lesions in the CEA failed to affect defensive burying and accompanying tachycardiac response as compared to sham-lesioned controls during the presentation of the electrified shock probe (unconditioned test). However, CEA lesioning attenuated the bradycardiac response and the immobility behavior during the late part of the test. Retention of this behavior one day after the exposure to the probe (conditioned test) was attenuated by the lesion. However, when the lesion was placed after the unconditioned test situation, retention of the burying was not affected, but the animals failed to show immobility behavior. These results, in agreement with former studies, suggest that the CEA is involved particularly in the organization and/or expression of the passive component of the behavior and the parasympathetic outflow during stress. The active component, i.e., burying behavior, and the accompanying tachycardiac response remains unaffected unless the acquisition of the stress response took place with damaged CEA.

Attenuated cardiovascular, neuroendocrine, and behavioral responses after a single footshock in central amygdaloid lesioned male rats

The effect of bilateral electrolytical CEA lesioning on behavioral, cardiovascular and neuroendocrine changes has been studied in male Wistar rats before, during and shortly after a brief aversive stimulus of an unavoidable footshock. Blood samples were withdrawn via a permanent heart catheter. Lesioning of the CEA abolished completely the immobility response normally seen after a footshock. Lesions failed to affect the early tachycardiac response compared to sham-lesioned controls, but the poststress recovery was attenuated, probably due to diminished vagal activation. Furthermore, the magnitude of the responses of all measured hormones (epinephrine, norepinephrine, corticosterone and prolactin) appeared to be attenuated in the lesioned rats. These results suggest that the CEA plays an important and general role in the behavioral, autonomic and hormonal output during a brief unavoidable, unconditioned footshock. This is in contrast with the selective role of the CEA in vagal (parasympathetic) and on inhibitory (immobility) behavioral responses following conditioning.

Central regulation of stress responses: regulation of the autonomic nervous system and visceral function by corticotrophin releasing factor-41

Our understanding of the role of CRF in mediating integrated endocrine, autonomic and visceral stress responses is rudimentary at best. Delineating the large number of neurochemical factors that influence the activity of CRF-containing hypophyseotrophic neurones offers one direction for future research in this area. Another approach might be to examine the neuropharmacological actions of transmitters which are co-localized within CRF-containing neurones. For example, CRF and dynorphin-related peptides coexist within a subpopulation of paraventricular neurones (Roth et al, 1983), suggesting the potential for their simultaneous release and possible functional interactions between them. Interestingly, CRF and dynorphin-related peptides exhibit reciprocal actions on the release of each other in vitro and in vivo. CRF stimulates the release of immunoreactive dynorphin from rat hypothalamic slices (Nikolarakis et al, 1986) while dynorphin A1-17 inhibits the basal secretion of immunoreactive CRF from rat hypothalami (Yajima et al, 1986). In vivo experiments demonstrate that i.c.v. administration of dynorphin A1-13 reduces basal and hypotension-induced secretion of CRF into hypophyseal portal blood (Plotsky, 1986). Recent studies suggest that, in addition to their interactions at the level of release, these peptides may also modify the CNS actions of each other on autonomic and cardiovascular function (Overton and Fisher, 1989b). Thus, CRF-induced elevations of arterial pressure, heart rate and plasma catecholamine levels are attenuated by co-administration of low doses of dynorphin A1-17. The reciprocal release actions and neuropharmacological interactions between CRF and dynorphin A1-17 suggest that local integration or perhaps feedback regulation of stress-induced autonomic and cardiovascular responses may be achieved by the co-release of multiple neurotransmitters from a single source. In summary, the combined anatomical, pharmacological and physiological data provide support for the involvement of CRF neuronal systems in mediating the integration of endocrine, autonomic, and visceral functions, particularly in response to stress. Future research in this area may contribute to our understanding of the neurobiology of CRF as well as the CNS mechanisms governing homeostasis.

Effects of 5-HT-1A receptor agonists on CRF-induced behavior

Buspirone (2.0 or 4.0 mg/kg) and 8-hydroxy-2-(di-N-propylamino)-tetralin (8-OH-DPAT) (0.25 or 0.5 mg/kg) were used to examine the effects of serotonin 1A receptor agonists on the behavioral response of rats to centrally administered corticotropin-releasing factor (CRF). Behavioral observations were done with animals in their home cages. Parameters measured included locomotor activity, grooming and food consumption. CRF alone increased locomotor activity. 8-OH-DPAT also increased locomotion in both saline control and CRF-treated rats. Buspirone had no effect on basal locomotion or on CRF-induced hyperactivity. Both buspirone and 8-OH-DPAT antagonized CRF-induced grooming. Food consumption by fasted rats was suppressed by ICV CRF. 8-OH-DPAT suppressed eating by both ICV CRF and ICV saline-treated animals, while buspirone was without effect. These results demonstrate differences between the two putative 5-HT-1A agonists in their effects on CRF-induced behaviour but also demonstrate that both suppress CRF-induced grooming.

The central amygdala is involved in the conditioned but not in the meal-induced cephalic insulin response in the rat

The central nucleus of the amygdala (CEA) is considered to be involved in the regulation of autonomic correlates of fear. Its involvement in the control of autonomic functions other than elicited by fear has received little attention. The effects of a bilateral electrolytical lesion of the CEA on feeding related insulin responses have been analyzed in male Wistar rats. The cephalic phase of the insulin response is a vagally mediated elevation of plasma insulin concentration during the first minute after meal onset, before any increase in plasma glucose can be noticed. This response can also be entrained to environmental stimuli. The insulin response elicited under these conditions is due to conditioning. CEA lesioning abolished the conditioned insulin response but not the early insulin elevation during the presentation of food. The CEA lesion failed to affect plasma glucose levels in both the meal-induced and conditioned test situations. To our knowledge this is the first study that shows that the CEA is also involved in the organization of conditioned metabolic endocrine responses.

Simultaneous localization of calcitonin gene-related peptide and neurotensin in rat central amygdaloid nucleus

The distribution of calcitonin gene-related peptide (CGRP) and neurotensin (NT)-like immunoreactivities (LI) was studied in rat central amygdaloid nucleus (ACe) with immunocytochemical double staining. A dense network of CGRP- and NT-immunoreactive (IR) nerve fibers and some NT-positive neurons were found in the lateral and lateral capsular subnuclei. Light microscopically CGRP-immunoreactive nerve endings were in close contact to most of the NT-immunoreactive neurons. Under the electron microscope CGRP-positive terminals formed symmetric axo-somatic synapses with part of the NT-IR neurons. These results indicate that the NT- and CGRP-containing neuronal systems are in contact with each other in the ACe. Both peptides have marked effects on the circulatory system when administered intracerebrally. Thus the NT-IR neuronal system receiving synaptic input from CGRP-IR nerve terminals may mediate the cardiovascular effects of these two peptides.

Aversive taste stimuli increase CGRP levels in the gustatory insular cortex of the rat

Calcitonin gene-related peptide-like immunoreactivity (CGRP-IR) was surveyed immunohistochemically in the insular cortex of the rat, and the levels of insular cortical CGRP-IR were measured with the radioimmunoassay method following intraoral stimulation with various taste stimuli. CGRP-IR was localized in nerve fibers within the agranular and dysgranular insular cortices. The CGRP-IR levels in the rostral (gustatory) part of the insular cortex were increased significantly by strongly aversive taste stimuli such as quinine hydrochloride and conditioned taste stimuli (NaCl and sucrose) which animals had been taught to avoid. The results suggest that CGRP in the gustatory insular cortex is concerned with rejection or avoidance behaviors to aversive taste stimuli.

Neuropeptides and catecholamines in efferent projections of the nuclei of the solitary tract in the rat

This study focuses on the involvement of catecholamines and nine different peptides in efferents of the nucleus of the solitary tract to the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and different parabrachial and hypothalamic nuclei in the rat. A double-labeling technique was used that combines a protein-gold complex as the retrograde tracer with immunohistochemistry. Catecholaminergic projection neurons were the most numerous type observed and projected mainly ipsilaterally to all targets studied. Most projections arose from areas overlying the dorsal motor nucleus, mainly the medial nucleus. Neurons synthesizing somatostatin, met-enkephalin-Arg-Gly-Leu, dynorphin B, neuropeptide Y, and neurotensin projected to all structures examined. Somatostatin and enkephalin immunoreactive projection cells were the most numerous. They were located in close proximity to each other, including all subnuclei immediately surrounding the solitary tract, bilaterally. Most dynorphin and neuropeptide Y immunoreactive projection cells were found rostral to that of enkephalinergic and somatostatinergic projections, and mainly in the ipsilateral medial nucleus. Neurotensinergic projections were sparse and from dorsal and dorsolateral nuclei. Substance P and cholecystokinin contribute to parabrachial afferents. The location of substance P immunoreactive projection cells closely resembled that of enkephalinergic and somatostatinergic projections. Projecting cholecystokinin immunoreactive cells were observed in dorsolateral nucleus. Bombesin immunoreactive cells in dorsal nucleus projected to either the parabrachial or hypothalamic nuclei. No vasoactive intestinal polypeptide-containing cells were detected. Thus, most catecholaminergic and neuropeptidergic efferents originated from different populations of cells. It is proposed that catecholaminergic neurons constitute the bulk of solitary efferents and that they may contribute to autonomic neurotransmission. Peptidergic neurons mainly form other subgroups of projections and may play a role in modulating the physiological state of the target nuclei.

Opioids in the systemic hemodynamic and renal responses to stress in spontaneously hypertensive rats

Endogenous opioid peptides have been implicated in the regulation of cardiovascular and renal function. We tested this hypothesis by examining whether the opioid antagonist naloxone alters the cardiovascular or renal responses produced by environmental stress (air stress) in conscious spontaneously hypertensive rats (SHR). Before naloxone administration, air stress produced significant increases in heart rate, mean arterial pressure, and renal sympathetic nerve activity, and it caused a decrease in urinary sodium excretion. After intravenous and intracerebroventricular administration of naloxone, the air stress-induced pressor and antinatriuretic responses were inhibited. Subsequent studies with a different opioid antagonist, the quaternary compound naltrexone methylbromide, also showed inhibition of the air stress-induced pressor and antinatriuretic responses and demonstrated opioid receptor specificity of this inhibition. Furthermore, since only intracerebroventricular and not intravenous administration of naltrexone methylbromide inhibited the pressor and antinatriuretic responses to air stress, a central nervous system site of action was established. The opioid antagonists caused inhibition of the pressor and antinatriuretic responses to air stress without affecting the air stress-induced increase in renal sympathetic nerve activity. Our investigations indicate that central endogenous opioid peptides contribute to the pressor and antinatriuretic responses that occur in conscious SHR during acute environmental stress.

The amygdalo-brainstem pathway: selective innervation of dopaminergic, noradrenergic and adrenergic cells in the rat

The present study investigated the organization and distribution of amygdaloid axons within the various brainstem dopaminergic, noradrenergic and adrenergic cell groups. This was accomplished via Phaseolus vulgaris leucoagglutinin lectin (PHA-L) anterograde tracing technique combined with glucose-oxidase immunocytochemistry to catecholamine markers (i.e. tyrosine hydroxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase). Injections of PHA-L within the medial part of the central amygdaloid nucleus resulted in axonal labeling within most catecholamine containing cell groups within the brainstem. The most heavily innervated catecholaminergic groups were the A9 (lateral) cells of the substantia nigra, the A8 dopaminergic cells of the retrorubral field and the C2 adrenergic cells of nucleus of the solitary tract. Amygdaloid terminals frequently contacted cells within these regions. A moderate amount of amygdaloid terminals were located within the rostral A6 (locus coeruleus) and A2 (nucleus of the solitary tract) groups. Amygdaloid terminal contacts were apparent on the majority of the rostral A6 and A2 neurons. Light or no amygdaloid terminal labeling was observed within the other brainstem catecholaminergic cell groups. Thus, the amygdala mainly innervates the A8 and lateral A9 dopaminergic cells of midbrain, rostral locus coeruleus (A6) noradrenergic neurons and the adrenergic (C2) and noradrenergic (A2) cells within the nucleus of the solitary tract. Selective innervation of these brainstem catecholaminergic systems may be important for integration of amygdaloid-mediated defensive and stress-induced behaviors.

The amygdala directly innervates adrenergic (C1) neurons in the ventrolateral medulla in the rat

The innervation of adrenergic (C1) neurons in the ventrolateral medulla by the central amygdaloid nucleus (Ce) was investigated using immunohistochemical detection of phenylethanolamine N-methyltransferase (PNMT) combined with anterograde tracing through Phaseolus vulgaris leucoagglutinin (PHA-L) transport and lesion-induced axonal degeneration. Injections of PHA-L into the medial Ce labelled axons in close proximity to PNMT-immunoreactive dendrites and somata in the ventrolateral medulla. The PNMT-immunoreactive neurons within the rostral part of the nucleus reticularis rostroventrolateralis were preferentially innervated by the amygdaloid terminals. Degenerating terminals formed synaptic contacts on PNMT-immunoreactive cells of the ventrolateral medulla in animals with lesions of the Ce. The synaptic contacts were mainly found on dendrites and were usually of the symmetrical type. The present findings provide evidence that cells within the amygdala directly innervate presumed adrenergic cells in the ventrolateral medulla. This pathway may be part of the anatomical substrates that are activated during amygdaloid-mediated sympathetic activity.

Brain neuropeptides: actions on central cardiovascular control mechanisms

The many peptides we have not considered (e.g. gastrin, motilin, FMRFamide, carnosine, litorin, dermorphin, casomorphin, eledoisin, prolactin, growth hormone, neuromedin U, proctolin, etc.) were omitted due to lack of information as far as any putative central cardiovascular effects are concerned. However, even for some of these peptide pariahs intriguing snippets of information are available now (e.g. ref. 85), although as we write, the list of possible candidates for investigation grows longer. On an optimistic note, it is becoming clear that many brain neuropeptides may have important effects on cardiovascular regulation. It seems feasible that 'chemically coded' pathways in the brain might be the neuroanatomical correlate of a 'viscerotopic' organization of cardiovascular control mechanisms, whereby the activity of the heart and flows through vascular beds are individually controlled, but in an integrated fashion, utilizing particular combinations of neurotransmitters and neuropeptides within the brain. Such possibilities can only be investigated, properly, by measurement of changes in cardiac output and regional haemodynamics in response to appropriate interventions, in conscious, unrestrained animals.